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You can also place the center speaker below a TV or projection screen, although on top is by far the more common position. Wherever you place it, the speaker should be aimed toward the listening position to produce the best frequency response there. Some models tilt up or down or have a support you can adjust for the correct angle.

Next come the left and right surround speakers. The rules here are a little different than for the front speakers because the surrounds are typically used to create diffuse, ambient sound in order to heighten the illusion of an all-encompassing sonic environment - especially with movie soundtracks. Many surround speakers are dipole or bipole designs that radiate from both front and back to enhance the sense of spaciousness.

But multichannel DVD-Audio or Super Audio CD music recordings tend to sound best when you use direct-radiating, or "monopole," speakers, since they often have smoother frequency response than dipoles and a less diffuse sound quality.

What kind of surround speakers should you go with? If you plan on using your system primarily for movies, I recommend a dipole or bipole design. If for music, use monopoles. If you want the best of both worlds, there are a few receivers that let you switch between two pairs of surround speakers.

Surround speakers should be placed to either side of the listening position and slightly to the rear - not in the back of the room unless absolutely necessary. They are usually mounted on the side walls, but placing them on stands works just as well. Avoid aiming dipole speakers directly at the listening position, since this will weaken the sense of a diffuse sound field. These speakers are best placed with their driver sides facing forward and backward, with the null side of the enclosure pointed toward the listener. Monopole speakers, on the other hand, are best placed on the side walls facing toward the listener but above ear level.

6.1-Channel Sound A number of 6.1-channel formats have appeared recently: Dolby Digital Surround EX and two flavors of DTS-ES (Extended Surround) - Discrete and Matrix. Each of these formats adds a back surround channel to the usual home theater configuration, using one or two additional speakers (and amplifier channels) to create a more realistic, quasi-360° sonic environment and smoother pans between the surround speakers.

If you're one of the lucky ones who own a 6.1-channel receiver, you'll want to set up your additional speaker or speakers along the rear wall, at the same height as the left and right surround speakers. If you opt for dipoles, have them fire to the left and right along the rear wall, with the null toward the listening position. (If this isn't satisfying, you can even try rotating them so that they fire toward the ceiling and floor.) Direct-radiating speakers should be aimed forward.

I'm Gonna Add Some Bottom No home theater system is complete without a subwoofer for the powerful sonic impact and realism that only true low-frequency extension can provide. It's sometimes said that you don't have to be as fastidious with setting up a sub as with your main speakers because frequencies below around 100 Hz are nondirectional. This isn't entirely true (unless you're planning on putting the subwoofer in the bathroom). Placing the sub in a room node will eliminate much of the bass, while placing it in an area that selectively reinforces bass might make it sound boomy. Experiment with placement for best results, and use common sense - don't place a sub too far away from the main front speakers or the imaging may be inconsistent.

I generally recommend starting with a corner placement and moving away from that only if you can't get proper balance using all the system's bass-management controls. Another approach is to set the subwoofer on a table at the listening position, so that its driver is at the same height as the listener's ears. Then go around the room on your hands and knees, listening to the bass at the same height that the subwoofer will be at once it's placed on the floor. Once you've found the spot where the bass sounds "tightest" (not boomy or mushy), place the sub there.